The present invention relates to an apparatus for regulating an energy system which is connected to a DC voltage, and to a method for operating such an energy system which is connected to a DC voltage.
It is known to operate electrical appliances by means of a DC voltage. In this case, the DC voltage provided is not always available to the voltage level required for the operation of an appliance. In this case, the DC voltage first needs to be matched by a suitable DC-to-DC converter. Such DC-to-DC converters are furthermore in special embodiments also capable of enabling galvanic isolation between the primary side at the input of the DC-to-DC converter and the secondary side at the output of the converter. For such isolated DC voltage conversion, the primary voltage on the input side is first converted via electronic switching elements into an AC voltage. Thereupon, the electrical energy can be transformed via a transformer. On the secondary side of the transformer, the transformed AC voltage can in turn be rectified and filtered, if required. An isolated DC-to-DC converter is known, for example, from the document DE 10 2008 022 910 A1. Said document discloses a method for operating a DC-to-DC converter over a large load range.
FIG. 1 shows a schematic illustration of an isolated DC-to-DC converter. A primary DC voltage is in this case first converted in an inverter 4 into an AC voltage. This AC voltage is supplied to the primary terminal of a transformer 1. The resulting output voltage at the secondary terminal of the transformer 1 is then rectified in a rectifier 5 and smoothed, if necessary. In the process, drive electronics 6 monitor the output voltage and, if required, adapt the driving of the inverter in such a way that an output voltage which is as constant as possible is achieved. If in the process the driving of the switches on the primary side of the DC-to-DC converter likewise takes place via suitable drive transformers 2 and 3, no voltage supplies for driving the DC-to-DC converter are required on the primary side.
If, however, relatively large voltage fluctuations occur on the primary side of the DC-to-DC converter, the output voltage is difficult to adjust stably when the voltage fluctuation on the primary side is not known. Therefore, for the regulation of a DC-to-DC converter, it is desirable to be able to sense the primary voltage and to incorporate the variation in the primary voltage in the regulation procedure.
In order to maintain the isolation between the primary side and the secondary side of the DC-to-DC converter, a voltage measurement on the primary side is very involved. For example, the voltage on the primary side can first be measured. For galvanic isolation, the measured value can then be transmitted in analog form by means of optical or magnetic coupling to the regulation system 6 located on the secondary side. For this, however, an additional supply voltage is required on the primary side.
Furthermore, it is also possible to convert the voltage on the primary side after the measurement directly into a digital signal and then to transmit this digital signal to the secondary side, for example via magnetic or capacitive coupling. However, this solution is very involved and results in relatively low dynamics owing to the analog-to-digital conversion.
A further alternative comprises a measurement of the primary-side voltage by means of a differential amplifier with a high resistance over the isolation barrier. This differential amplifier needs to have an extremely high resistance, however. Furthermore, with this solution unavoidable leakage resistances are to be expected.
There is therefore a requirement for an improved apparatus for regulating an energy system, such as an isolated DC-to-DC converter, for example, in which voltage fluctuations on the primary side can be detected and compensated for in a simple manner.